Organic electroluminescent device

ABSTRACT

The invention relates to an organic electroluminescent device ( 1 ), which is easily connectable to a socket in a cost-effective and reliable way. The organic electroluminescent device ( 1 ) comprising an electroluminescent layer stack ( 3, 4, 5 ) on top of a substrate ( 2 ) and a cover lid ( 6 ) encapsulating the electroluminescent layer stack ( 3, 4, 5 ), wherein the cover lid ( 6 ) comprises a least one electrical feedthrough ( 61 ) to electrically contact the electroluminescent layer stack ( 3, 4, 5 ) and at least one fastening element ( 62 ), where the at least one fastening element ( 62 ) is arranged to fasten the organic electroluminescent device ( 1 ) to a housing ( 8 ) such that forces to a backside of the cover lid ( 6   b ) during fastening of the housing ( 8 ) are minimized.

FIELD OF THE INVENTION

The invention relates to the field of organic electroluminescent deviceswith cover lids comprising fastening elements and to light emittingunits comprising such organic electroluminescent devices

BACKGROUND OF THE INVENTION

Organic electroluminescent devices (or diodes) are devices, whereorganic molecules emit light when a driving voltage is applied to suchorganic electroluminescent devices (OLEDs). The OLEDs typically comprisea transparent substrate with a layer stack deposited on top of thesubstrate comprising an organic layer stack between two electrodelayers, typically a tansparent anode layer on top of the substrate and areflective cathode on top of the organic layer stack. Since the organicmoleculs are sensitice to moisture and oxygen, the layer stack isencapsulated by a gas tight cover lid sealed on top of the substrate.Depending on the structure of the anode and/or the electricalfeedthrought, the cover lids might be sealed partly on top of the anodeor any other electrically conductive material. In order to operate theOLED, the OLED has to be placed into a socket providing an electricalconnection to a power source supplying driving voltages in the order ofa few volt, e.g. 2-10 V. The socket-base system of an OLED (as the base)and the socket being also the OLED holder shall be easily to be used,especially the OLED shall be connected to the socket easily.

Document U.S. 2010/0046210 discloses a socket-base system for OLEDs,where the OLEDs are fastened to a mount via mechanical/electricalcouplers arranged at the backside of an OLED frame comprising the OLEDas a plurality of protrusion to be inserted into complementary openingsin the holder/housing with a one-directional movement. The interlockmechanism resembles that of the LEGO building blocks. In anotherembodiment, OLED devices are dircetly coupled to each other by pipe-likecouplers fitting into each other or by protrusions fitting incorresponding metal inserts of adjacent OLEDs avoiding any housing forthe OLEDs. These couplers are additional components to be added to theOLED devices. In contrast to that there is a demand to reduced thenumber of required components in order to provide a cost-effectivesocket-base system.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an organicelectroluminescent device, which is easily connectable to a socket in acost-effective and reliable way.

It is a further object of the present invention to provide a lightemitting unit comprising such organic electroluminescent device.

This object is achieved by an organic electroluminescent devicecomprising an electroluminescent layer stack on top of a substrate and acover lid encapsulating the electroluminescent layer stack, wherein thecover lid comprises at least one electrical feedthrough to electricallycontact the electroluminescent layer stack and at least one fasteningelement, where the at least one fastening element is arranged to fastenthe organic electroluminescent device to a housing such that forces to abackside of the cover lid during fastening of the housing are minimized.The cover lid commonly acts as an encapsulation for theelectroluminescent layer stack of the organic electroluminescent device(OLED). In the present invention, additional functionalities are addedto the cover lid, since the cover lid is simultaneously used to fastenthe OLED to a housing. Commonly OLED devices comprise frames used totightly fasten the OLED on one hand to the frame and to establish aconnection between frame and housing. In this invention frames can beavoided reducing the required parts within a socket-base system, wherethe hosing acts as a socket providing electrical contacts and acts as acavity at least partly accommodating the OLED, which reduces themanufacturing costs. Furthermore, the OLED itself (via the cover lid) isequipped with fastening elements making the connection to a housing fastand easy avoiding the use of OLED frames. The fastening element mayexceed the substrate in a direction perpendicular to the light emissiondirection. Alternatively the fastening element may protude in adirection opposite to the light emission direction. The fasteningelement may in both cases be attached in such a way to the cover lid,such that during fastening of the housing to the cover lid direct forcesto the backside of the cover lid may be avoided. The latter means thatthe forces applied during fastening of the housing to the cover lid arepreferably transferred via the side walls of the cover lid to thesubstrate. Bending of the backside of the cover lid extending across thesensitive electroluminescent layer stack may thus be reduced or evenavoided. The direct fastening of OLEDs into the housing improves thereliability of a socket-base system, because only a single connection isrequired in contrast to double connections of OLED-to-frame andframe-to-housing. A reduced number of required connection reduces therisk of connection problems and therefore will improve the reliabilityof the light emission from the OLED.

The organic electroluminescent device may utilize organic smallmolecules or polymers to produce light. Accordingly, OLEDs may bereferred to as small molecule organic light emitting devices (SMOLEDs)or polymer light emitting devices (PLEDs). However, SMOLEDS arepreferred because of their better light emission performance. Thesubstrate is made of a transparent material, e.g. glass or plastic,having two essentially parallel surfaces. The side of the substratefacing towards the electroluminescent layer stack is also denoted asbackside in the following. The side of the substrate opposite to theback side is denoted as light emitting side (or front side). Theelectroluminescent layer stack comprises at least two electrodes asanode and cathode and an organic light emitting layer in between. Inother embodiments, there might be a plurality of organic layers arrangedbetween the electrodes, such as hole transport layer, electron transportlayer, hole blocking layers, electron blocking layers, one or more lightemitting layers, e.g. comprising a host material with embedded lightemitting molecules. A large number of different electroluminescent layerstacks comprising a different number/type of layers is known to skilledpeople, which are able to chose a suitable electroluminescent layerstack in dependence on the desired application. Typically, the electrodedeposited on top of the substrate is a transparent anode, e.g. made ofindium-tin-oxide (ITO). The other electrode, typically the cathode, ismade of a reflective metal, e.g. Al. In some embodiment, there areadditional layers present between the transparent anode and thesubstrate in order to improve the light outcoupling behaviour of theOLED. Additional hard layers may be deposited locally on top of thetransparent anode in order to enable a contacting of the cathode fromthe side of the cover lid. Such hard layers have to be made of anelectrically insulating material in order to avoid shorts between anodeand cathode caused by the contacting of the cathode, e.g. with acontacting wires or a pin, form the backside (side of the cover lid).

In an embodiment the fastening element exceeds the substrate in adirection perpendicular to the light emission direction in order toavoid forces which may be applied to the electroluminescent layer stackduring fastening the cover lid to the housing. The cover lid may exceedthe subtrate in all directions, since the electroluminescent layer stackis contacted through the cover lid (backside of the cover lid) via atleast one electrical feedthrough, also denoted as back-contacting. Anelectrical feedthrough comprises a conductive path from the inner sideof the cover lid (facing towards the electroluminescent layer stack) tothe outer side of the cover lid (or backside, the side opposite to theinner side). The electrical path is usually electrically insulatedagainst the cover lid. Such insulation is required, if the cover lid ismade of metal. In case of back-contacting, no contact areas on top ofthe backside of substrate outside the cover lid are required to contactthe electroluminescent layer stack. Subsequently the cover lid canexceed the substrate partly or along all directions parallel to thebackside of the substrate. The light emitting side is the side of thesubstrate, where at least the majority of light is emitted to theenvironment, and the side of the substrate opposite to the lightemitting side is denotes as backside of the substrate. The lightemission through to the light emitting surface of the substrate has aLambertian characteristic, where the the maximum of light is emittedperpendiculat to the light emitting surface of the substrate, alsocalled as light emission direction in the following. The term“exceeding” denotes the dimension of cover lid being longer than thecorresponding dimension of the subtrate (or poking out of the substate)along a direction perpendicular to the light emission direction, whichis perpendicular to the surface of the light emitting side of thesubstrate.

The cover lid is made of any material suitable to be equipped withelectrical feedthroughs and rigid enough to be able to fasten the OLEDto a housing. The fastening element may be the rim of the cover lidexceeding the substrate entirely or partly as the fastening element.Alternatively, the cover lid may comprise differently shaped fasteningelements of a suitable shape to fasten the OLED to a housing. Thematerial of at least the fastening means may be metal or plastic. Theremaining material of the cover lid may be metal or plastic as well as aceramic material or glass. The cover lid is sealed to the substrate inorder to establish an encapsulation by a sealing material, e.g. acontiguous line of glass frit (non-conductive) or conductive epoxy glue,around the electroluminescent layer stack, to provide a gas tight sealagainst moisture and oxygen. The term “fasten the OLED” denotes theinserting the OLED into a housing, which provides a tight fit of theOLED to the housing, preferably independently from the location and/ororientation, where the housing is placed. Therefore at least thefastening element exceed the substrate of at least 1 mm, preferably morethan 5 mm, to provide a tight fit to the housing.

In another embodiment the fastening element is a male or female part ofa bayonet connector or is at least one element of the group of elementscomprising a plate, a flap, a latch, or a hook. Here, the bayonetconnector (or bayonet mount) is a fastening mechanism consisting forexample of a male side with one or more pins, and a female receptor withmatching L slots and spring(s) to keep the two parts locked together. Tocouple the two parts, the pin(s) on the male are aligned with theslot(s) on the female and the two pushed together. Once the pins reachthe bottom of the slot, the two parts are turned in opposite directionsto guide the pin across the bottom of the L shaped slot. The spring thenholds the pin in position to prevent it from backing out. To disconnect,the two parts are pushed together to overcome the spring whilst twistingslightly to reverse the locking turn. The strength of the joint relieson the shear strength of the pins and the strength of the L slots whichhold the pins in place when locked. A practised user can connect themquickly and they are not subject to cross-threading. In otherembodiments the bayonet connector may be shaped differently within thescope of this invention. Alternatively a plate as a fastening elementrequires a slot or cavity to be inserted into at the housing, the sameholds for flaps and latches. Hooks can be inserted into correspondingholes or bolts or behind pins to fix the OLED to a housing. All thesefastening elements enable a fast locking of the OLED to a housing and ondemand a fast removal of the OLED from the housing. The fast fasteningand/or removal may be required at OLED walls equipped with OLED tiles,where the arrangedmant of the OLEDs shall be changed on demand.

In another embodiment the fastening element is attached at a backside ofthe cover lid or is attached to a sealing part of the cover lid. Incases, where the gap between substrates of adjacent OLED present in ahousing for multiple OLED shall be as small as possible, preferablywithout any gap between adjacent OLEDs, the fastening elements arearranged at the backside of the cover lid enabling a wider freedom ofmechanical design for the housing to provide a tight fit together withthe closely arranged substrate of adjacent OLEDs. The backside of thecover lid denotes the side of the cover lid facing away from thesubstrate. On the other hand, fastening elements present at the sealingpart of the cover lid enables to fasten the OLED to a housing with asmall buidling depth, e.g. with flat cover lids having a backsidearranged in a closer distance to the substrate. The sealing part denotesthe area of the cover lid, where the lid is sealed to the substrate.

In another emodiment at least the fastening element of the cover lid ismade of a magnetic material. A magnetic material can be fastened to acorresponding magnet present in a housing without the need of anyadditionally required mechanical locking means. Fixing OLEDs to housingwith the use of magnets is realized in prior art by placing OLED inframes, which comprise magnets as additional components. Than themagnets of the frames are attached to metal parts present in thehousings. In this invention, the cover lid made of magnetic material canbe used instead of additional magnets to fasten the OLED to a housing.As an example, steel might be used as a magnetic material for the coverlid. The fastening can be achieved by placing one or more magnets of asuitable strength in the housing. The OLED can easily be reversiblyattached to the housing. The advantage is, that no modification of theOLED cover lid is required to enabled a tight fit of the OLED in thehousing.

In another embodiment at least one of the fastening elements, at leastparts of the remaining cover lid and a sealing material are made of anelectrical conductive material, preferably the cover lid is essentiallymade of electrical conductive material. Here, the cover lid might beused as an electrical path connected to one of the electrodes of theelectroluminescent layer stack via the electrically conductive sealingmaterial (e.g. epoxy glue with a conductive filler) when at least partlysealed on top of this electrode. A cover lid essentially made ofelectrical conductive material might be used not only to contact theelectrode, but also to distribute the current applied to this electrodeand therefore acting as a shunting structure. This shunting structureprovides an improved homogeniety of the brightness of the OLED. The term“essentially” shall denote the entire cover lid excluding the areas ofthe cover lid, where electrical feedthroughs are present.

In another embodiment the volume between the cover lid and the substrateis filled with an inert fluid or gel providing a good heat conductivitybetween the electroluminscent layer stack and the cover lid, preferablythe fluid or gel is a fluorinated fluid or silicone gel, more preferablya Sylgard 3-6636 silicone dielectric gel or a Dow Corning fluorogelQ3-6679 dielectric gel. OLEDs are currently operated at rather low powerdensities of about 30 W/m², with luminance values of typically 1.000cd/m². In the future, much higher values of up to 10.000 cd/m² areenvisaged. These higher luminance levels will lead to a substantialself-heating of the OLED, which requires a better cooling of the OLED.Metalic lids can provide a sufficient heat transfer to a housing forcooling purposes, if the heat conductivity between electroluminescentlayer stack and metalic lids is sufficient. Currently, the volume insidethe cover lid is filled with gas providing a too low heat conductivity.A fluid or gel filling the volume will improve the heat transfer fromthe electroluminescent layer stack to the cover lid. The fluid or gelhas to be chemically inert against the organic layers within theelectroluminescent layer stack. Therefore a fluorinated fluid of gel ispreferred.

In another emodiment the at least one feedthrough is arranged as a pinextending to the outside of the cover lid or as a contact area suitableto be contacted with an electrical contact from the outside. Suchcontact from the outside might be a contact pin. Such shapes of thefeedthrough at the backside of the cover lid are easy to be connectedwith a corresponding electrical path provided from a housing. Thecontact area denotes an area of a size significantly larger than a crosssection of a pin. A pin exceeds the outer surface of the cover lid,while a contact area may by a protrusion in the outer side of the coverlid or may be one the same level as the outer side of the cover lid.Preferably, the contact area has a flat and smooth surface. The pinmight have a rounded or sharp tip at its top.

The invention further relates to a light emitting unit comprising atleast one organic electroluminescent device according to the presentinvention and at least one housing, wherein the housing is adapted toprovide electrical contacts to the organic electroluminescent device andcomprises one or more receiving elements adapted to the fastening meansto fasten the organic electroluminescent device via the fastening meansto the housing. A housing could be any cavity of any shape suitable toat least partly accommodate the OLED. To be able to fasten the OLED, thehousing has to comprise receiving elements adapted to provide a tightfit to the correspondingly shaped fastening element of the OLED. Thereceiving element might be made of any suitable material such as metal,plastic or any other material. Preferably the one or more receivingelements and the at least one fastening element establish a bayonetconnector or the one or more receiving elements are arranged to fastenthe at least one fastening elements of the organic electroluminescentdevice arranged as at least one element of the group of elementscomprising a plate, a flap, a latch, or a hook. The electrical contactsin the housing are further connected to a power source in order to applya driving voltage to the OLED via the electrical contacts within thehousing. The power souce may be integrated in the housing or may belocated externally. The power source may be any power source suitable toprovide a driving voltage in the order of a few volts, e.g. 2-15V. Theconnection to the power source may be established by wires connected(e.g. welded or soldered) to the electrical contacts or may beestablished by other conductive paths (e.g. conductive layers) connectedto the electrical contacts. The electrical contacts itself may beconductive layers, wires, pins or other suitable means to establish anelectrical contact to the OLED, where the term “electrical contact”always denotes the separate contacting of anode and cathode of theelectroluminescent layer stack of the OLED via the cover lid of theOLED, either directly to the cover lid and/or via electricalfeedthroughs arranged within the cover lid.

In another embodiment the housing comprises at least one magnet,preferably at least parts of the one or more receiving elements arearranged as magnets, in order to fasten the cover lid of the organicelectroluminescent device, where at least the fastening element of thecover lid is made of a magnetic material. The magnets have to arrangedat suitable locations of the housing adapted to the shape of the coverlid and/or the fastening elements. Suitable magnets are common permanentmagnets. Preferably at least one of the magnets provide an electricalcontact to the cover lid when the magnetic material is also electricallyconductive. In case of magnets made of electrically non-conductivemagnetic material, these magnets might be coated with an electricalcoating to provide a magnet suitable to be used as electrical contact.This will avoid additional electrical contacts within the housing toconnect the OLED to a power source. The magnets of the housing caneasily be contacted from its backside with a wire or other electricalconnection means. The mechanical fixation, which is simultaneously alsoat least one of the electical contacts further simplifies theconstruction of the OLED and the socket-base system of OLED and housing.A magnet as electrical contact provides a reliable contact even in caseof slight mechanical movements of housing and/or OLED.

In another embodiment the one or more receiving elements are made of anelectrical conductive material in order to provide an electrical contactto the organic electro-luminescent device via the at least one fasteningelement. The receiving elements are connected to the cover lid to fastenthe OLED. If the receiving elements are simultaneously used aselectrical contacts, the functions of mechanical fixation and electricalconnection can be integrated in one component, which saves componentcosts. In case of two electrically separated receiving elementsconnected to a power source and a suitable cover lid comprisingseparated electrically conductive paths connecting anode and cathode ofthe electroluminescent layer stack separately (e.g. via the sealedlocally conductive cover lid and the conductive sealing material to theanode and via an electrical feedthrough in the cover lid to the cathode,alternatively via two separate feedthroughts in the cover lid) the OLEDcan easily be electrically connnected to a power source via thereceiving elements and the cover lid.

In an alternative embodiment the housing comprises at least one pin madeof electrical conductive material, preferably the pin being springloaded, to electrically contact the cover lid and/or at least oneelectrical insulated feedthrough within the cover lid to provide anelectrical contact to anode and/or cathode of the organicelectroluminescent layer. Here one electrical contact (or electricalconnection) to at least one feedthrough is not established via thereceiving elements but to the backside of the cover lid, whereelectrical feedthroughs are located. This offers the possibility tomanufacture the receiving elements as a single component, e.g. made ofmetal and e.g. providing an electrical contact to the cover lid via thefastening element. The second electrical contact is established bydirect contacting the electrical feedthrough within the cover lid. Incase of a feedthrough providing a contact area, a pin can easily providean electrical connection between contact area of the feedthrough and apower source be touching the contact area. In this case the cover lidcould be made of metal being electrical conductive entirely (withfeedthrough(s) electrically insulated against the cover lid) or has tocomprise suitable conductive parts. Such conductive parts may beestablished by a cover lid partly made of metal or by depositing asuitable conductive layer on top of the cover lid to provide anelectrical contact to one of the electrodes, e.g. to the anode.Alternatively, both anode and cathode may by connected via two separatefeedthroughs contacted by two separate pins within the housing. In thelatter case the cover lid not necessarily have to be made of metal. Alsonon-conductive material can be used as cover lid material. In case of aspring loaded pin, the spring will apply a sufficient force to the pinto establish a reliable continuous electrical contact of the pin to thecontact area. The spring force has to be adapted to a suitable force notto bend the cover lid touching the electroluminescent layer stack.People skilled in tha art are able to chose a sufficient spring forcedepending on thicknesses amd sizes of the cover lid and the distancebetween cover lid and the electroluminescent layer stack.

In another embodiment the housing comprises a heat sink structure incontact to at least parts of the cover lid of the organicelectroluminescent device. OLED are currently operated at rather lowpower densities of about 30 W/m², with luminance values of typically1.000 cd/m². In the future, much higher values of up to 10.000 cd/m² areenvisaged. These higher luminance levels will lead to a substantialself-heating of the OLED, which requires a better cooling of the OLED.Metalic lids can provide a significant heat transfer to a housing(significant cooling of the OLED), if the heat conductivity between theOLED and the housing is suifficient. A heat sink in contact to a metalcover lid provides such good heat conductivity. The heat sink structurecould by any suitable structure, e.g. a heat sink structure as appliedto semi-conductor circuits. In a preferred embodiment the heat sinkstructure is a heat paste filling at least partly the gap between coverlid and housing to avoid an air gap between OLED and housing. Such airgaps would reduce a heat transfer drastically, up to a factor of 8000. Adirect contact between OLED and housing, e.g. made of metal in the areain contact with the heat paste and optionally connected to another heatsink arranged on the backside of the housing, provides a good heattransfer away from the OLED. Ceramic based, metal based and carbon-basedheat pastes are on the market today. The thermal conductivity of suchheat pastes could be up to 200 W/mK or more, e.g. 218 forberylliumoxide-paste or 170 for aluminumnitride-paste, which is abouthalf of the thermal conductivity of copper (380 W/mK) or silver (429W/mK). The pastes commonly comprise metal oxide and/or nitride particlessuspended in silicone thermal compounds. Preferably the heat paste isarranged ouside the area of electrical feedthroughts and/or electricalcontacts (e.g. metal pins), because heat pastes might be electricallyconductive and would cause shots between anode and cathode contacts ifcovering cover lid and feeedthroughs as a single layer.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows two embodiments of an organic electroluminescent device anda housing according to the present invention with (a) the fasteningelements arranged at the sealing part of the cover lid, and (b) thefastening elements arranged at the backside of the cover lid.

FIG. 2 shows another embodiment of the housing comprising magnets.

FIG. 3 shows an embodiment of a light emitting unit according to thepresent invention with the receiving element of the housing as one ofthe electrical contacts.

FIG. 4 shows another embodiment of a light emitting unit according tothe present invention with two electrical contacts in the housingarranged as spring loaded pins.

FIG. 5 shows another embodiment of a light emitting unit according tothe present invention with the receiving element of the housing as oneof the electrical contacts and a spring loaded pin as the otherelectrical contact arranged in the housing.

FIG. 6 shows another embodiment of a light emitting unit according tothe present invention with two electrical contacts in the housingarranged as spring loaded pins, where the cover lid is made ofnon-conductive material.

FIG. 7 shows another embodiment of a light emitting unit according tothe present invention comprising a heat paste as a heat sink structurebetween housing and organic electrolumninescent device.

FIG. 8 shows another embodiments of an organic electroluminescent deviceand a housing according to the present invention with the fasteningelements arranged at the backside of the cover lid protuding in adirection opposite to the light emission direction.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows two embodiments of an organic electroluminescent device 1and a housing 8 according to the present invention with (a) thefastening elements 62 arranged at the sealing part 6 s of the cover lid6, and (b) the fastening elements 62 arranged at the backside 6 b of thecover lid 6. Here, the organic electroluminescent device 1 comprises anelectroluminescent layer stack 3, 4, 5 on top of a substrate 2 and acover lid 6 encapsulating the electroluminescent layer stack 3, 4, 5.The substrate is made of a transparent material, such as glass orplastic (e.g. PMMA or PET). The electroluminescent layer stack comprisesat least a first transparent electrode 3 on top of the substrate 2,typically the anode 3 made of indium-tin-oxide (ITO), an organic lightemitting layer 4 or layer stack 4 on top of the first electrode 3 and asecond electrode 5 on top of the organic light emitting layer 4 or layerstack 4, typically the cathode 5 made of a reflective material such asaluminum. The light emitting layer 4 may comprise an organic hostmaterial and embedded light emitting molecules. In several cases thelayer 4 comprises additional layers forming a layer stack 4. Theseadditional layers may comprise one more more layers of the group of holetransport layer, electron transport layer, hole blocking layer, electronblocking layer, additional organic light emitting layer(s). Severalelectroluminescent layer stacks are known. People skilled in the art areable to chose the appropriate electroluminescent layer stack for theparticular application. The cover lid 6 could be made of any materialsuitable to encapsulate the electroluminescent layer stack 3, 4, 5against moisture and oxygen from the environment. However, this materialshould be at least suitable to accommodate electrical feedthroughts 61in a gas tight way in order to contact the anode 3 and the cathode 5.The cover lid 6 is connected to the substrate 2 and/or to the anode 4 ontop of the sustrate by a conductive sealing material 64. The sealingmaterial 64 (e.g. epoxy glue) could be doped with metal particals tobecome electrically conductive. The cover lid 6 further comprises atleast one electrical feedthrough 61 to electrically contact at least oneof the electrodes 3, 5 and at least one fastening element 62 exceedingthe substrate 2 in a direction perpendicular to the light emissiondirection 7. In FIG. 1 there are two fastening elements 62 arranged tofasten the organic electroluminescent device 1 to a housing 8, whichcomprises two corresponding receiving elements 82 to accommodate thefastening elements 62. The material of the receiving elements 82 is anymaterial suitable to fasten the OLED 1, e.g. metal or plastic or otherlike wood etc. The fastening structure is shown only schematically inFIG. 1. The two receiving elements 82 and the two fastening elements 62may establish a bayonet connector or may be arranged to fasten the twofastening elements 62 of the organic electroluminescent device 1arranged as plates, flaps, latches, or hooks. The fastening elements 62may be fixed into the cooresponding part of the bayonet connector viasprings pushing onto the fastening elements 62. People skilled in theart are able to chose the appropriate shape of a bayonet connector. Afastening element 62 as latch, plate or flap would be inserted into acorresondingly shaped cavity as the receiving element 82. Theinsertation could be performed via a translational motion or via arotational mortion, depending on the shape of the housing 8, the OLED 1and/or the cover lid 6, 62. The material of the fastening elements 62could be any material suitable to fasten the OLED 1 to the housing 8.Preferably the fastening elements 62 are made of the same material asthe remaining cover lid 6. More preferably the cover lid 6 comprisingthe fastening elements 62 is a single piece component 6. After insertingIN the organic electroluminescent device 1 into the housing 8, a lightemitting unit is formed. When a driving voltage is applied to theorganic electroluminescent device 1 by a suitable power source 10 (e.g.comprising further drivers etc.), the OLED 1 will emit light 7 throughthe substrate 2. The main direction of the light emission 7 isperpendicular to the front side of the substrate 2 facing away from theelectroluminescent layer stack 3, 4, 5. The fastening elements 62 arearranged perpendicular (vertical) to the direction of light emission 7exceeding the substrate 2 in order to fit into corresponding receivingelements 82 of the housing 8. Depending on the shape of the housing 8,the fastening elements 62 may be arranged at the sealed part 6 s of thecover lid 6 close to the sealing material 64 or may be arranged at thebackside 6 b of the cover lid 6. In the first case, the recevingelements 82 may be arranged to end at the same level as the front sideof the substrate 2 in order to provide a smooth surface of the lightemitting unit. In the latter case, the OLED 1 will poke out of thehousing 8, which could be desired in other cases. The electricalcontacts in FIG. 1 are established by two electrical contacts 81 locatedin the housing 8 opponent to the backside 6 b of the cover lid 6 wheninserted IN into the housing 8. The contact for the anode is arranged tocontact the cover lid 6 somewhere outside the feedthrough 61. Here thecover lid is made of metal. Together with an electrically conductivesealing material 64 and an anode 3 being in electrical contact to thesealing material 64, the positive voltage provided by the power source10 is applied to the anode 3 via a wire connected to the electricalcontact 81 within the housing 8 being in electrical contact (indicatedby the dashed arrow CA) with the metal cover lid 6 further in electricalcontact with the anode 3 via the electrical conductive sealing material64 being in electrical contact to the anode 3. The negative voltage isprovided by the power source 10 via a wire connected to the electricalcontact 81 within the housing 8 being in electrical contact to thefeedthrough 61 (insulated against the metal cover lid as indicated bythe white area around the gray area 61) as indicated by the dashed arrowCC, further being in electrical contact with the cathode 5 via theelectrical bridge 61 a between feedthrough and cathode. Such bridgecould be established e.g by conductive glue 51 or by a wire arrangedbetween the conductive glue 51 and the feeedthrough 61. In order not todamage the electroluminescent layer stack 3, 4, 5, especially not tocause a short between anode 3 and cathode 5, there might be a hardnon-conductive layer arranged locally underneath the conductive glue 51between anode 3 and organic light emitting layer 4. The feedthrough 61might comprise a contact pin or might be arranged as a flat conductivesurface to be connected to the electrical conatcs 81 of the housing 8.

FIG. 2 shows another embodiment of the housing 8 comprising magnets 91,92. The magnets 91 may be arranged at any suitable position to fastenand/or to support the fastening (in addition to the fastening providedbe the receiving elements 82) of the OLED 1 in the housing 8. The shownhousing with two magnets 91 is only one example. In other embodimentswithin the scope of the present invention the number, size and locationof the magnets might vary. In an alternative embodiment the magnets 92are arranged as parts of the receiving elements 82. Both alternativesare able to fasten the cover lid 6 of the organic electroluminescentdevice 1 when the fastening elements 62 and/or the cover lid 6 are madeof a magnetic material, e.g steel or any other suitable metal.

FIG. 3 shows an embodiment of a light emitting unit according to thepresent invention with the receiving element 62 of the housing 8arranged as one of the electrical contacts 81 as indicated with the grayarea of the left receiving element 82. In contrast to FIG. 1, thisembodiment requires only one electrical contact 81 at the backside ofthe cover lid 6. The double functionality of the receiving element 82providing a tight fit of the OLED 1 and providing an electrical contact81, e.g. to the anode 4, allows to reduce the number of components forthe housing 8. The contact 81 at the backside of the cover lid isestablished by a pin 81 a in contact to the feedthrough 61.

FIG. 4 shows another embodiment of a light emitting unit according tothe present invention with two electrical contacts 81 in the housing 8arranged as two spring loaded pins 81 b. The electrical connectionbetween power source 10 and OLED (anode 3, cathode 5) corresponds to thedescription of the electrical connection in FIG. 1. The spring loadedpins 81 b enable to apply a certain maximum pressure to the cover lid 6in order to avoid a bending of the cover lid eventually resulting in acover lid touching the electroluminescent layer stack 3, 4, 5, whichcould damage the electroluminescent layer stack 3, 4, 5. Furthermore,the spring loaded pins 81 b will provide a reliable electricalconnection to feedthroughs 61 and/or cover lid 6 even in case of smallmechanical movements of the OLED 1 in the housing 8, since the springsprovide an elastic connection.

FIG. 5 shows another embodiment of a light emitting unit according tothe present invention with the receiving element 82 of the housing 8 asone of the electrical contacts 81 and a spring loaded pins 81 b as theother electrical contact 81 arranged in the housing 8. FIG. 5 is anadvatageous combination of the emodiments shown in FIGS. 3 and 4.

FIG. 6 shows another embodiment of a light emitting unit according tothe present invention with two electrical contacts 81 in the housing 8arranged as two spring loaded pins 81 b. The electrical connectionbetween power source 10 and OLED (anode 3, cathode 5) corresponds to thedescription of the electrical connection in FIG. 1. The spring loadedpins 81 b enable to apply a certain maximum pressure to the cover lid 6in order to avoid a bending of the cover lid eventually resulting in acover lid touching the electroluminescent layer stack 3, 4, 5, whichcould damage the electroluminescent layer stack 3, 4, 5. Furthermore,the two spring loaded pins 81 b will provide a reliable electricalconnection to the two feedthroughs 61 even in case of small mechanicalmovements of the OLED 1 in the housing 8, since the springs provide anelastic connection. In this embodiment, the cover lid does not have tobe conductive, since the anode 3 is contacted to the spring loaded pinsimilar like the cathode 5, with an electrical bridge 61 a betweenfeedthrough and anode 3. Such bridge could be established e.g byconductive glue 51 or by a wire arranged between the conductive glue 51and the feeedthrough 61. Alternatively to a non-conductive cover lid 6,the cover lid 6 might also be conductive. Furthermore the sealingmaterial 64 might be non-conductive, e.g. glass-frit. Here, allcombinations of conductive/non-conductive cover lids 6 and/orconductive/non-conductive sealing materials 64 might be used, becausethe electrical contacting of cathode 5 and anode 3 are provided throughfeedthroughs 61 a electrically insulated against the cover lid 6.

FIG. 7 shows another embodiment of a light emitting unit according tothe present invention comprising a heat paste 11 as a heat sinkstructure between housing 8 and organic electrolumninescent device 1.Ceramic based, metal based and carbon-based heat pastes are available onthe market today. The thermal conductivity of such heat paste could beup to 200 W/mK or more, e.g. 218 for berylliumoxide-paste or 170 foraluminumnitride-paste, which is about half of the thermal conductivityof copper (380 W/mK) or silver (429 W/mK). The pastes commonly comprisemetal oxide and/or nitride particles suspended in silicone thermalcompounds. In case of electrically conductive heat pastes 11, the heatpaste has to be arranged ouside the area of electrical feedthroughts 61and/or electrical contact 81, 81 a, 81 b, as shown in FIG. 7. Thehousing may further comprise a conventional heat sink (not shown here)at the backside of the housing (side of the housing facing away from theOLED 1), which is in direct contact to the heat paste or the hosuning inbetween the heat paste and the heat sink is made of metal (howeverinsulated against the electrical contact 81). To improve the heattransfer, also the electroluminescent layer stack 3, 4, 5 should bethermally coupled to the cover lid 6. Usually, the encapsulated volume63 is filled with gas having a poor thermal conductivity. The heattransfer from the electroluminescent layer stack 3, 4, 5 to the coverlid 6 can be significantly improved by filling the volume 63 with aninert fluid or gel providing a good heat conductivity between theelectroluminscent layer stack 3, 4, 5 and the cover lid 6, preferablythe fluid or gel is a fluorinated fluid or gel, e.g. a silicon gel.Suitable gels are for example Sylgard 3-6636 silicone dielectric gel orDow Corning fluorogel Q3-6679 dielectric gel.

In an alternative embodiment of the present invention shown in FIG. 8,the fastening elements 62 protrude in a direction opposite to the lightemission direction 7. The fastening elements 62 are arranged directlyabove the sealing part of the cover lid 6 s in order to avoid or atleast limit forces which may be applied to the electroluminescent layerstack by means of the backside of the cover lid 6 b during fastening ofthe cover lid 6 to the housing 8. This allows an easy fastening of thecover lid 6 by inserting the protruding fastening elements 62 intocorresponding receiving elements 82 in the housing 8. The fasteningelement 62 may extend around the whole circumference of the cover lid 6such that the cross section of the cover lid may look like a H as shownin FIG. 8 in order to provide a stable and reliable fastening of thehousing 8. Alternatively, two or more fastening elements 62 may beprovided at the edge of the cover lid 6 protruding in a directionopposite to the light emission direction 7. The protruding fasteningelements 62 may also be used as feedthrough 6l as shown in FIG. 8 inorder to provide electrical contacts to the anode and the cathode.

In other embodiments not explicitly shown here, the number of electricalcontacts 81 may be more than 2. In an embodiment, the cover lid 6comprises multiple feedthroughs 61 in order to contact the cathode 5 inparallel to improve the current distribution within the cathode 5. Inanother emodiment, all receiving elements 62 are arranged as electricalcontacts 81 to the cover lid 6 in order to improve the currentdistribution for the anode 3. In another embodiment, the cover lid 6 maycomprise multiple feedthroughs 61 in order to contact multiple anodes 3and multiple cathode 5 of a structured OLED 1 comprising multipleelectrically separated electroluminescent layer stacks 3, 4, 5. Inanother embodiment the cover lid 6 may comprise multiple feedthroughs 61in order to contact multiple intermediate electrodes (not shown here)present in between of vertically stacked electroluminescent layer stacksof so-called stacked OLEDs.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments. Other variationsto the disclosed embodiments can be understood and effected by thoseskilled in the art in practicing the claimed invention, from a study ofthe drawings, the disclosure, and the appended claims. In the claims,the word “comprising” does not exclude other elements or steps, and theindefinite article “a” or “an” does not exclude a plurality. The merefact that certain measures are recited in mutually different dependentclaims does not indicate that a combination of these measures cannot beused to advantage. Any reference signs in the claims should not beconstrued as limiting the scope.

LIST OF REFERENCE SIGNS

-   1 organic electroluminescent device-   2 substrate-   3 first electrode, typically the anode-   4 organic light emitting layer (stack)-   5 second electrode, typically the cathode-   51 conductive glue-   6 cover lid-   61 feedthrough within the cover lid-   61 a conductive bridge to the electrical feedthrough-   62 fastening elements-   63 volume encapsulated from the cover lid-   64 sealing material, e.g. glass frit or epoxy glue with conductive    filler-   6 s sealing part of the cover lid-   6 b backside of the cover lid-   7 light emission direction-   8 housing-   81 electrical contact-   81 a electrical contact as pin-   81 b electrical contact as spring loaded pin-   82 receiving element-   91 magnet within the housing-   92 magnet arranged within the receiving element of the housing-   10 power source-   11 heat sink structure, especially a heat paste-   CC electrical contact to the cathode-   CA electrical contact to the anode-   IN inserting the OLED into the housing

1. An organic electroluminescent device comprising an electroluminescentlayer stack on top of a substrate and a cover lid encapsulating theelectroluminescent layer stack, wherein the cover lid comprises at leastone electrical feedthrough to electrically contact theelectroluminescent layer stack and at least one fastening element, theat least one fastening element being arranged to fasten the organicelectroluminescent device to a housing such that forces applied to thecover lid during fastening of the housing are minimized by transferringthe forces via the side walls of the coverlid to the substrate such thatbending of a backside of the cover lid is reduced.
 2. The organicelectroluminescent device according to claim 1, wherein the fasteningelement constitutes a part of a bayonet connector.
 3. The organicelectroluminescent device according to claim 1, wherein the fasteningelement is attached at a backside of the cover lid or is attached to asealing part of the cover lid.
 4. The organic electroluminescent deviceaccording to claim 1, wherein the fastening means extends beyond thesubstrate in a direction perpendicular to the light emission direction.5. The organic electroluminescent device according to claim 1, at leastthe fastening element of the cover lid comprises a magnetic material. 6.The organic electroluminescent device according to claim 1, wherein atleast one of the fastening elements at least parts of the remainingcover lid and a sealing material comprise an electrical conductivematerial.
 7. The organic electroluminescent device according to claim 5,wherein the volume (between the cover lid and the substrate is filledwith an inert fluid or gel providing a good heat conductivity betweenthe electroluminescent layer stack and the cover lid.
 8. The organicelectroluminescent device according to claim 1, wherein the at least onefeedthrough is arranged as a pin extending to the outside of the coverlid or as a contact area suitable to be contacted with an electricalcontact from the outside.
 9. A light emitting unit comprising at leastone organic electroluminescent device according to claim 1 and at leastone housing, wherein the housing is adapted to provide electricalcontacts to the organic electroluminescent device and comprises one ormore receiving elements adapted to the fastening means to fasten theorganic electroluminescent device via the fastening means to thehousing.
 10. The light emitting unit according to claim 9, wherein theone or more receiving elements and the at least one fastening elementestablish a bayonet connector or the one or more receiving elements arearranged to fasten the at least one fastening elements of the organicelectroluminescent device arranged as at least one element of the groupof elements consisting of a plate, a flap, a latch, and a hook.
 11. Thelight emitting unit according to claim 9, wherein the housing comprisesat least one magnet, in order to fasten the cover lid of the organicelectroluminescent device, where at least the fastening element of thecover lid comprises a magnetic material.
 12. The light emitting unitaccording to claim 11, wherein at least one of the magnets provide anelectrical contact to the cover lid.
 13. The light emitting unitaccording to claim 9, wherein at least one of the one or more receivingelements are made of an electrical conductive material in order toprovide an electrical contact to the organic electroluminescent devicevia the at least one fastening element.
 14. The light emitting unitaccording to claim 9, wherein the housing comprises at least one pinmade of electrical conductive material, the pin being spring loaded, toelectrically contact the cover lid and/or at least one electricalinsulated feedthrough within the cover lid to provide an electricalcontact to a anode and/or cathode of the organic electroluminescentlayer.
 15. The light emitting unit according to claim 9, wherein thehousing comprises a heat sink structure in contact to at least parts ofthe cover lid of the organic electroluminescent device.
 16. The organicelectroluminescent device according to claim 1, wherein the fasteningelement is selected from a group consisting of: a plate, a flap, alatch, and a hook.
 17. The organic light emitting unit according toclaim 15, wherein the heat sink structure comprises a heat paste fillingat least partly the gap between cover lid and housing and outside thearea of electrical feedthroughts and/or electrical contacts.